This chapter is from the book

This chapter is from the book

Some aspects of our stylesheets are of a global nature that we must consider
before we delve into the details of template instruction execution and
behaviors. This chapter overviews the aspects of our environment in which we use
our XSLT processor from the perspectives of the stylesheet contents, the
serialized output (if any), and the operator invoking the processor.

All explicitly declared stylesheets follow a required shape of container and
top-level (container children) elements. Methods are also specified for
including arbitrary information in a stylesheet file, useful for supplemental
information for processing, or as documentation of the stylesheet content.

The stylesheet can declare its desire for values of certain parameters of the
output serialization that influence the contents of the reified result node
tree.

In addition, there are a number of ways available to communicate with an XSLT
processor that is interpreting a stylesheet resource against a source resource.
Communication to the processor can be engaged at invocation as well as from the
processor during execution.

Finally, this chapter reviews aspects of the transformation environment that
cannot be controlled by the operator or the stylesheet. It is important to
understand the limitations of what can be asked for or even supported by the
XSLT processor.

This chapter includes discussion of the following XSLT instructions regarding
the transformation environment in which a stylesheet is used.

Instructions for wrapping the content of a stylesheet are as follows.

<xsl:stylesheet>

encapsulates a stylesheet specification.

<xsl:transform>

encapsulates a stylesheet specification.

Instructions for serializing the result tree are as follows.

<xsl:namespace-alias>

specifies a result tree namespace translation.

<xsl:output>

specifies the desired serialization of the result tree.

Instructions for communicating with the operator are as follows.

<xsl:message>

reports a stylesheet condition to the operator.

<xsl:param>

supplies a parameterized value from the operator.

5.1 Stylesheet basics

5.1.1 The stylesheet document/container element

Two identical and interchangeable choices for the document element are:

<xsl:stylesheet>

<xsl:transform>

They can also be used as a container element for a stylesheet embedded in
another context.

They may use id="unique identifier".

It identifies the stylesheet when there are multiple ones from which
to choose.

The use of this XML IDattribute is outside the scope of the Recommendation.

It could be used as a fragment identifier by the stylesheet association
processing instruction or by other techniques to identify a given stylesheet
among many.

Controls available on container element or any literal result element are:

exclude-result-prefixes="whitespace-separated-prefixes"

scope of influence is all descendent elements in stylesheet;

this declaration indicates which stylesheet namespace prefixes are not
expected in the result, thus are not to be included in the stylesheet
tree;

a list of whitespace-separated namespace prefixes specifies prefixes
that are to be explicitly excluded from the stylesheet tree (using #default
as the name to reference the default namespace, which is sometimes unofficiallycalled
the null namespace);

user-specified prefixes and associated namespace declarations are often
used in XSLT stylesheets (but not desired in the result) for various purposes
such as:

top-level documentation,

embedded structured data,

named XSLT constructs;

recall that copying an element node from the stylesheet to the result
will copy all attached namespace nodes, thus stylesheet namespace declarations
can easily end up in the result tree;

a stylesheet wrapper-element namespace declaration is typically used
for top-level namespace usage, thus the document element of the result
will typically end up with the same declarations;

this exclusion declaration tells the XSLT processor to not include the
specified namespace nodes on descendent nodes of the stylesheet tree;

this exclusion declaration has no effect on namespace nodes of the source
tree,

extension-element-prefixes="whitespace-separated-prefixes"

scope of influence is all descendent elements in stylesheet;

this declaration indicates which stylesheet namespace prefixes are
instruction prefixes;

a list of whitespace-separated namespace prefixes specifying prefixes
that are extension namespaces to be recognized by the XSLT processor
(using #default as the name to reference the default namespace);

recall that everything that is not an instruction is considered
to be a literal result element;

elements prefixed with the namespace prefix associated with the
XSLT URI are interpreted as instructions;

this declaration tells the XSLT processor what other prefixes are
to be interpreted as instructions because they are extension elements
required by the stylesheet;

the processor need not implement the extension elements (detailed
in Chapter 6).

Child elements of the document or container element are referred to
as "top-level" elements.

If present, the following must occur before all other top-level elements:

xsl:import

see Chapter 6.

If present, the following (listed alphabetically) may occur in any order
as top-level elements:

xsl:attribute-set

see Chapter 7,

xsl:include

see Chapter 6,

xsl:key

see Chapter 8,

xsl:decimal-format

see Chapter 8,

xsl:namespace-alias

see this chapter,

xsl:output

see this chapter,

xsl:preserve-space

see Chapter 3,

xsl:strip-space

see Chapter 3,

xsl:template

see Chapter 4.

The following are used not only as top-level elements, while all others
listed above are only used as top-level elements:

xsl:param

see Chapter 6,

xsl:variable

6 see Chapter 6.

Because an XSL stylesheet is an XML document 

XML comments can be used to provide documentation about the stylesheet,

all XML comments and processing instructions found in an XSL stylesheet
are ignored.

Note that some XML editing tools may leave processing instructions in
files for remembering locations such as the last cursor position.

Adding richly marked up documentation to a stylesheet:

allows the stylesheet to be run through a documenting stylesheet to
extract the documentation in any fashion desired,

is accomplished by including non-XSLT constructs as top-level elements
(children of the stylesheet document element) provided that the default
namespace is not used as the namespace for such constructs, as in the
following example:

When this particular stylesheet is run with itself (or any XML file)
as the source, the XSLT processor will assign the "xslo:"
prefix's URI used in the result tree with the URI for the "xsl"
prefix as indicated in the <xsl:namespace-alias> instruction,
thus using the XSLT URI when the result tree is serialized as XML markup: